Background: Second-generation (gen) ALK tyrosine kinase inhibitors (TKIs) are standard first- and second-line therapies in patients (pts) with advanced ALK+ non-small cell lung cancer (NSCLC). After progression on second-gen TKI(s), standard options include platinum (PT)-based chemotherapy (chemo) or the third-gen ALK TKI lorlatinib. The efficacy of PT-based chemo is established in treatment-naive pts but is undefined in pts who have failed prior ALK TKIs. Here we evaluate the efficacy of PT/pemetrexed (pem)-based chemo in pts with ALK+ NSCLC refractory to second-gen TKIs. Methods: A retrospective study was performed at three institutions. Pts were eligible if they had advanced ALK+ NSCLC refractory to ≥1 second-gen TKI, and received PT-pem-based chemo. Medical records and imaging were reviewed to determine outcomes. Results: Among 55 eligible pts, chemo regimens included: PT/pem (31/55, 56%), PT/pem/bevacizumab (bev) (6/55, 11%), PT/pem/PD-1 inhibitor (3/55, 5%), PT/pem with ALK TKI (8/55, 15%), PT/pem/bev with TKI (6/55, 11%), and PT/pem/PD-1 inhibitor with TKI (1/55, 2%). Pts had received one (6/55, 11%), two (38/55, 69%), or more (11/55, 20%) prior TKIs. Six pts (11%) previously received adjuvant or neoadjuvant chemo. Radiographic data for response evaluation was available for 39 pts. Among 36 pts with measurable baseline disease, confirmed ORR was 31% (11/36; 95% CI, 16-48%); 13 (36%) had stable disease. The median duration of response was 5.4 months (95% CI, 1.5-7.1 months). The median progression-free survival (PFS) for the entire cohort was 4.0 months (95% CI, 2.8-4.6 months). Chemo (PT/pem +/- bev or PD-1 inhibitor) plus ALK TKI (n = 15) was associated with a significant increase in PFS compared to chemo without TKI (n = 40) (median PFS 6.8 vs 3.2 months; HR 0.306; p = 0.002). Similarly, PT/pem plus ALK TKI (n = 8) was associated with increased PFS compared to PT/pem without TKI (n = 31) (median PFS 6.8 vs 2.9 months; HR 0.358; p = 0.036). Conclusions: The efficacy of PT-pem-based chemo is limited after failure of second-gen ALK TKIs but may be higher in pts who receive chemo plus ALK TKI, suggesting a potential role for ongoing ALK inhibition. The modest benefit of PT-pem-based chemo highlights the need for other therapeutic strategies for pts refractory to second-gen TKIs.